How to implement a clean up method after request finish process in a spring boot application for clean data such as thread locals
I try with ServletRequestListener.requestDestroyed api, but it does not get hit after the request finish
One possible answer is that you have neglected to register the listener. The Servlet javadocs say:
In order to receive these notification events, the implementation class must be either declared in the deployment descriptor of the web application, annotated with WebListener, or registered via one of the addListener methods defined on ServletContext.
There may be other ways to implement this using Spring; e.g. using a handler intercepter; see Remove ThreadLocal object within a Spring MVC website?
If you were using plain servlets (without the Spring MVC infrastructure), another approach would be to do the cleanup in your servlet's service method or the doXxx methods. Or in a Filter in front of the servlet.
Actually I am trying to understand the DispatcherServlet and came to know that it is following the FrontController Design Pattern.
While trying to understand the FrontController design pattern came across this link
FrontController from Oracle Doc reference
Not much understood as I am beginner, but few things I understood Like Below
If we don't have FrontController we often try to duplicate the code in multiple controller like authentication and Authorization. And because of which maintainability becomes a big issue if we want to change something in future. So having frontController in place we can move the basic functionality to frontController and changes can be done easily.
When I explained Same thing in the interview he asked me what are those basic functionalities. I told Internalization, viewResolver, Authentication, Authorization etc. And now again asked consider like there is no dispatcher Servlet how do you handle those functionalities in each controller?
Since am basically a Desktop Application developer I couldn't answer for his next question.
So here are my questions
Firstly, is my understanding correct?
If my understand is correct, how to answer for the second question of the Interviewer? Which is consider like if there is no dispatcher Servlet how do you handle those functionalities in each controller? means asked me to write some pseudo code of the common functionalities. Which I couldn't as I am swing developer. Could someone please explain me, with some sample code which we repeat across the controller and now with dispatcher we could avoid.
If we Start comparing DispatcherServlet with frontController Design Pattern can we say like LocaleResolver, HandlerMapping, ThemeResolver, ViewResolver, HandlerExceptionResolver, HandlerAdapter, MultipartResolver etc. are Helper classes for DispatcherServlet?
The front controller design pattern means that all requests that come for a resource in an application will be handled by a single handler and then dispatched to the appropriate handler for that type of request. The front controller may use other helpers to achieve the dispatching mechanism.
Front Controller design pattern could be implemented by either of following two ways.
Using Servlet
Using Filter
Spring Framework implemented FrontController Design Patter using DispatcherServlet for intercepting each request and delegate to responsible controller to process the request.
If interviewer asks you, what happened if you don't have DispatcherServlet then how you manage all these authentication and authorization things, you can simply say that I can define a Filter which will intercept each request. Filter should be responsible for dispatching,authentication and authorization thing. Struts uses Filter to implement FrontController Design pattern.
(1) FrontController is simply the central place where all the external requests are received by and pass each of those requests to the appropriate handler. As you have explained since this is the central place for all the requests, it can be used to perform all the common things like security, logging etc.
(2) DispatcherServlet is the actually the front controller of Spring MVC. It intercepts each request and then dispatches each to the appropriate controller which has been registered in Spring Application Context.
consider like if there is no dispatcher Servlet how do you handle
those functionalities in each controller ?
For this one, I don't think this question implies that you need to write same code in each controller. (If it does, it cannot be a good idea)
You can do something like implementing a separate service which would do those common things (cross cutting concerns) for you can orchestrate all in coming requests.
Front Controller Definition
The front controller is responsible for handling all the requests for
a website. For web application developers, it can be a very useful
structure, as it allows the developers the flexibility and the ability
to reuse the code without having to add again and again.It provides a single point of action to handle the all coming requests to the J2EE web application, it forwards the request to specific application controller to access model and view for presentation
tier resources.
lets check the functionality of the Dispatcher Servlet to see if it is exactly the front end:
Consider the diagram below taken from https://docs.spring.io/spring/docs/3.0.0.M4/reference/html/ch15s02.html:
As you can see in the preceding diagram, the front controller is introduced for the
MVC pattern. It is implemented as a javax.servlet.Servlet servlet such as ActionServlet in struts, FacesServlet in JSF, and DispatcherServlet in Spring MVC. It handles the incoming requests, and delegates the requests to the
specific application controller. That application controller creates and updates the model, and delegates it to the front controller for rendering. Finally, the Front Controller determines the specific view, and renders that model data.
Now Consider the step as:
A user clicks on the browser or submits a web form of the application. The
request leaves the browser, either with some additional information or with
common information. This request lands at Spring's DispatcherServlet, which is a
simple servlet class as other java-based web applications. It is a Front
Controller of the Spring MVC framework, and funnels all the incoming requests
through the single point. The Spring MVC framework centralizes the request
flow control by using this Front Controller.
A user clicks on the browser or submits a web form of the application. The
request leaves the browser, either with some additional information or with
common information. This request lands at Spring's DispatcherServlet, which is a
simple servlet class as other java-based web applications. It is a Front
Controller of the Spring MVC framework, and funnels all the incoming requests
through the single point. The Spring MVC framework centralizes the request
flow control by using this Front Controller.
Once a particular application controller is decided by Spring's DispatcherServlet
with the help of the handler mapping configuration, DispatcherServlet dispatches
that request to the selected controller. This is the actual controller responsiblefor processing information according to the user's request and its parameters.
Once a particular application controller is decided by Spring's DispatcherServlet
with the help of the handler mapping configuration, DispatcherServlet dispatches
that request to the selected controller. This is the actual controller responsiblefor processing information according to the user's request and its parameters.
Once a particular application controller is decided by Spring's DispatcherServlet
with the help of the handler mapping configuration, DispatcherServlet dispatches
that request to the selected controller. This is the actual controller responsiblefor processing information according to the user's request and its parameters.
Spring MVC's DispatcherServlet renders the model to the view, and generates a
user-readable format of the model's information
Finally, that information creates a response, and returns it to the user's browser
by DispatcherServlet.
So The Spring MVC module provides out-of-the-box front controller pattern implementation by introducing the org.springframework.web.servlet.DispatcherServlet class. This is a simple servlet class, and the backbone of the Spring MVC framework. And this Servlet is integrated with the Spring IoC container to benefit the Spring's dependency pattern. Spring's web framework uses Spring for its own configuration, and all controllers are Spring beans. you can see the spring doc https://docs.spring.io/spring/docs/3.0.0.M4/reference/html/ch15s02.html that admitted the usage of front controller design pattern in DispatcherServlet
Answers specifically to your questions:
yes your understanding is okay but for a better view refer to my description
when there is no DispatcherServlet you need to define something to take care of the functionality you need and the best thing is to write a filter including your logic of authentication and authorization
These are not refer as Helper classes as it has it's own definition in OOP, you can consider them components playing part in front controller design pattern implemented version of Spring
More Info:
Majority of the definition comes from the book Spring 5 Design Patterns by Dinesh Rajput, you can refer this book for more info
I have many Servlets deployed on my server.
e.g.
servlet1
servlet2
I also have filter: Filter, with the url pattern "/*".
Filter catches all requests like localhost:8080/something except these ones localhost:8080/servlet1,localhost:8080/servlet2.
My question is following: How should i configure filter to catch all requests to all Servlets?
Thanks in advance.
Your configuration is correct.
However, I guess in your case you deployed your application as someting.war, so would only be able to catch requests to http://localhost:8080/someting/*, all the other requests won't go through your application.
So my guess is that you need to configure your container, to use your war as default reference.
I tried using Basic Authentication by changing the server.xml config of Tomcat 6.0 but it did not worked: BASIC authentication in jersey JAX-RS service and Tomcat 6.0 getting failed
Hence I am opting a way where no server specific config is needed and I can add up the roles directly in my code (either client or server; not sure about theavailable options).
Please provide me some ideas about the possible options for setting the user roles so that I can authenticate my Web Service methods using the #RolesAllowed annotation.
You need to go back and figure out why your security constraints weren't working. Maybe start with the default file realm before moving on to JDBC realms. #RolesAllowed in an annotation that triggers behavior in the container.
If you really want to do it yourself (a bad idea) they you'd probably start by creating a custom servlet filter that implemented the entire basic http challenge mechanism. Next you'd have to replace the SecurityContext provider in Jersey.
They "thing" that enables #RolesAllowed in jersey is this: http://java.net/projects/jersey/sources/svn/content/trunk/jersey/jersey-server/src/main/java/com/sun/jersey/api/container/filter/RolesAllowedResourceFilterFactory.java Which, by the way, don't forget to add as an init-param to your jersey servlet. The RolesAllowedResourceFilterFactory gets its security info from an injected SecurityContext which I'm sure at some point just delegates off to the Servlet API for credential info.
So basically if you don't want to take the time to get security constraints working you are going to end up replacing most of the chain...like I said, a bad idea.
The features on application servers are there to keep you from having to spend time creating infrastructure code, if you write your own infrastructure code you're going to have a bad time.
In the config file, there are lots of elements: flow-executor, flow-registry, flow-builder-services, viewFactoryCreator, FlowHandlerAdapter, FlowHandlerMapping, etc.
In what order do they work?
When a request comes in, the servelet will dispatch it to a handler, then I guess the spring web flow framework will somehow parse the flow and return a view. But how exactly does the spring web flow framework handle the request? And in what order do those elements defined in the config file work?
Here is a nice image of the request lifecycle taken from the link. Also here is an article giving you the life-cycle events.
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